Resonant cavity oscillator



April 25, 1944. E. G. UNDER RESONMTl cAvITY oscIL'LAToR l Original Filed Nov. 30, 1958 v Snoentor Ernest G.L1,nder

Patented Apr. 25, 1944 RESONANT CAVITY OSCILLATOR Ernest G. Linder, Philadelphia, Pa., assigner to Radio Gorporation of America, a corporation of Delaware Original application November 30, '1938, Serial No.

243,211, new Patent No. 2,233,263, dated February 25, 194i.

Divided and this application (Bctober 1S, 119453, Serial No. 361,707

l Claim.

This application is a division of.U. S. Patent 2,233,263 which issued February 25, 1941 on yapplication Serial No. 243,211, filed November 30, 1938, for Resonant cavity oscillators which application was assigned to the same assignee as the instant application.

This invention relates to ultra high frequency oscillators and more specially to ultra high frequency resonant cavity oscillators.

The term ultra high frequencyoscillations is generally applied to electromagnetic oscillations having a frequency of the order of 500 megacycles per second and upward. At thel higher frequencies, for example, 3000 megacycles, it has been `difficult to generate powerful oscillations. This `diiculty has been due to thespace characteristics of the thermionic tubes which are emi ployed. The prior art devices have been lrnown` as magnetron and Barkhausen Kurz oscillators. In these oscillators, the radio frequencypotentials are applied to the electrodes by means of resonant circuits.

The difficulties of generating radio frequencyV oscillations corresponding to a wave length of 10 centimeters will be appreciated by considering the physical size of a magnetron oscillator in which the anode electrode is a cylinder of the order of 2 millimeters radius and one centimeter length. In this arrangement, the anode is subjected to intensive heat when even low power oscillations are. generated. i

Thus, it is quite apparent that 'the space limitations of the thermionic oscillators of the prior art have prevented the generation of more than about 10 watts of ultra high frequency oscillatory energy. I propose to avoid structural limitations by employing tube elements which are not con nected by resonant circuits andl which do not' themselves oscillate. ln other words', the radio frequency potentials will not be applied to the tube elements which will further remove theV restrictions of size. In place of resonant circuits. I propose to employ a cavity which will resonate to oscillations 'of a predetermined frequency. The cavity may have aA size corresponding to a predetermined number of wave lengths. oscillatory' energy established within the cavity may be collected by an appropriately arranged conductor upon which the wavesy induce electromotive forces of the desired frequency.

As used'in this specification, the term free electrons is applied to electrons within the field` and external to the conductors. The free electrons are of two types: in-phase and out-of- The.

fore been practical.

to free electrons which subtract energy. Outof-phase electrons is the term designating free electrons which deliver their energy of motion.

It is one of the objects of the invention to provide means for generating ultra high frequency oscillations of greater power than has hitherto- Another object of the invention is to provide means for establishing oscillations within a resonant cavity. A still further object is to arrange thermionic tube elements within a resonant cavity whereby free electrons y establish resonant oscillations within the cavity.

A still further object is to provide means for creatingfree electrons within a cavity which is adjusted to establish therein standing electric waves.

The invention will be described by referring to the accompanying drawing in which Figures 1 and 1A are schematic diagrams of one embodiment-of the invention, and Figures 2 and 2A are schematic circuit diagrams of the preferred embodiment of the instant invention.

Referring to Fig. l, Within one end l of a hollow metallic cylinder t are suitably arranged on an insulator a lattice-like cathode 'l and an accelerating electrode 9. The cathode is energizedby a source of power it and the accelerating electrode is made positive with respect to the cathode by a battery i3.' The end portion of the cylinder is surrounded by a solenoid l5 which isy energized by a battery ll. The opposite end of the cylinder 3 includes a movable end portion i9 which is hermetically Asealed to lthe cylinder by means of a bellows 2L The end plate is coupled to a screw 23 which is used to adjust the position of the movable end plate i9. A coupling loop E5 is inserted within the cylinder through suitable insulators.

` The operation of the device is as follows: Electrons emitted by the cathode 'l proceed toward the accelerating electrode 9. Some of the elec- .trons will reach the electrode, but most, due to the deflection of the magnetic` eld, will be projected past the electrode toward the walls of the cylinder 3.

Upon reachingl the 4neighborhood of the cathode in a region roughly diametrlcally opposite to their place of emission, their radial motion will be reduced to zero and then reversed, and they will again be attracted towards the'accelerating electrode. Thus an oscillatory motion in a radial direction will be established.. Ari electron swarm will be formed about the electrode 9. The swarm consists of radially oscillating electrons, upon phase. In-phase electrons is the` term applied ,Il which a comparatively slow angular procession collected. The angular electron motion does not contribute directly to the establishment of the electric field oscillations. These oscillations are caused 'by the y radial component of electron motion. y

cal envelope. -Free electrons are set up within the resonant cavity by the cathode 8l, control grid 89 and electr e 9|. It will be observed that thev electrode 9 is biased negatively with respectto the cathode B1; therefore, the electrons approaching the electrode 9| will be repelled and will reenter the cavity. 'I'he reenter- .ing out-of-phase electrons will give up energy .to raid in the creation of or to strengthen the The oscillating electrons in the swarrrr` will radiate energy into the surrounding space inthe form of an electro-magnetic wave, whose frequency corresponds to the frequency of their own oscillatory motion, and whose electric vector is parallel to their own direction of motion. If

the cavity is of suitable dimensions, standing waves will be set up. The electric ileld thus established will react upon the electrons in the swarm. l Y

Originally (i. e., 'before the formation of a standing wave),l the electrons osciilate with a randomdistribution of phases. However, due to the reaction of the electric field, a grouping is caused. Some electrons will be moving in phase withthe electric oscillations of .'the field. These will gain energy and their amplitude of motion will increase. Their orbits will thus soon penetrate beyond the cathode 'l into the space between the cathode 1 and the cavity wall. 'I'his is a field free space insofar as nonoscillating fields are concerned, and all electrons reaching it will immediately travelto the cavity wall and be collected. Thus, in-phase electrons tend to be rapidly removed from( the swarm. On the other hand, electrons which oscillate 180 out of phase are constantly moving in an A. C. field which opposes their motion, and hence lose energy and remain much longer within the ren gion adjacent the cathode. This lost energy of motion appears as energy of electromagnetic field oscillations. These electrons are eventually collected by the accelerating electrode 9.

Although, for the sake of clarity, the above discussion has been applied only to in-phase electrons and electrons 180 out of phase, it actually applies to all electrons. This follows, since all electrons may be put into one of two classes (1), those which are in phase during most of a cycle, and (2) those which are out of phase during most of a cycle. It is obviousl that the grouping effect will occur for those two classes in much the same manner as for electrons in phase or out of phase during the entire cycle, as described above.

It should be understood that the magnetic field, potential of the electrodes and size o f the resonant cavity should be adjusted to obtain the optimum oscillations within the cavity. The electric oscillations thus generated induce electromotive forces in the coupling loop whose terminals are connected to an antenna, transstanding waves which are established as previously described. In rthis arrangement, the standing waves established within the cavity are partially spherical in form. No load circuit is shown, but it should be understood that the load circuit may take the form of a pickup coil, antenna or the like.

Thus the invention has been described as a resonant cavity oscillator. I am aware that G. C.

Southworth, in his U. S. Patent 2,129,713, has

described ultra high frequency oscillators which are positioned within a wave guide. The oscillators usedby Southworth are of the conventional type. 'I'he radio frequency potentials established on the oscillator elements radiate waves which travel through the wave guide. As previously explained, my invention relates to a new form of oscillator in which the elements of the tthermionic device create clouds of free electrons some of which deliver energy directly to create and maintain standing waves within a resonant cavity.

In the above-described devices, the resonant cavities have dimensions large compared to a `wave length. The resonant cavity cylinders will be able to handle large cathode emission currents and very high accelerating electrode potentials.

l Large amounts of heat can be dissipated, since the accelerated electrons strike the external internal portion of the cylinder, and its entire surface serves to radiate the heat produced. The

electrodes (cathodes and grid) are nonoscillating and thus consideration of electrode capacity and inductance play no part. 'Ihese electrodes are limited in size only by geometrical consideration. It is evident that the currents, voltages and power involved are all much greater than those utilizable by any previous type of device operating at such high frequencies.

I claim as my invention:

An ultra high frequency oscillator including a resonant chamber of spherical shape having a pair of reentrant portions including apertures, at least one tubular conductive member surrounding one of said apertures and extending from said chamber into one of said reentrant portions, means for emitting free electrons, means for focusing said electrons, means for projecting said electrons through said apertures and through said chamber, means including an elec- .trode disposed outside'of said cavity but within said one of said reentrant portions thereof and Within said tubular member for phasing said electrons so that out-of-phase electrons will deliver their energies to establish and maintain spherical waves within said chamber, and means for biasing said electrode negatively with respect to said electron emitting means for repelling electrons approaching said electrode so that said repelled electrons will reenter said cavity in proper phase to sustain oscillations.

' ERNEST G. LINDER. 

